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Need some help trouble shooting kx450f

Discussion in 'The Garage' started by Mellowyellow, Mar 7, 2013.

  1. Mellowyellow

    Mellowyellow XS650 Addict

    Hi guys,

    I know its not a xs but ive got some issues with a kx450f. I thought i would ask you guys because any dirt bike forum seems to be loaded with bad info.

    So here goes.......

    Bike was overheated end of last season (i could hear the rad boiling)

    Getting bike ready for spring (changed oil, set the valves, front fork seals, tires )

    -fired bike up and once warm it will back fire when reving.
    -at higher rpms i can tell its missing and not running correct.
    -then after about 5 minutes of running on stand rad starts boiling again.
    -when reving (even when warm) seems to smoke lots (blue).

    -So i checked anti freeze and there is no oil in it. (good sign)
    -checked oil no anti freeze in it (good sign)
    -ran bike with cap off and coolant is returning to rad and no bubbles.

    I thought it might be a head gasket but im not sure.

    Head gasket?

    Im lost guys. I would hate to drop it off at the stealership! Hope someone can help.
  2. Mellowyellow

    Mellowyellow XS650 Addict

    Just pulled the water pump, looks fine.

    still stumped!
  3. XSLeo

    XSLeo XS650 Guru Top Contributor

    Being that the KX450F is a Kawasaki and water cooled I don't know much about them. I might put KX450F forum in my search engine and try a few of the places that come up.
    I did and there seems to be many forums that talk about your bike.
    Sorry I can't be more help. Others may have more knowledge on your bike, if so they will chime in.
  4. Mellowyellow

    Mellowyellow XS650 Addict

    Hey Leo,

    Thanks, ive been doing as much googling as i can hahaha. Im 90 percent sure its a head gasket and maybe a warped head too. Im just dreaming and hoping some smart guy will chime in and have a super cheap simple fix hahaha.

    I have another 650 in the corner maybe i should throw out that kawi junk and put the right engine in there haha.

  5. mrtwowheel

    mrtwowheel Honda Etched On Brain Top Contributor

    There must be a thermostat, test it, hot water in pan with thermometer method.

  6. angus67

    angus67 Welder's penetrate deeper!!

    Thats what Im thinking, too. although you may have smoked your rings.
  7. yamamunn

    yamamunn XS650 Enthusiast

    Do not ever/never let a 4 stroke mx bike idle for 5 minutes on stand. I race moto have owned 3 -4 strokes 03 yz450, 09 yz 450 and now 2013yz450 if I sit on the line @ idle waiting for the gate to drop even after 2 minutes the pipe will start too glow red! as far as far as backfire if you are running it in cold weather and it is set for warm weather it will run lean and backfire usually this can be adjusted with the air screw located on bottom of float bowl, check to make sure your hot start is working this too can cuse backfire when bike is running pull your hot start in it should increase the idle as it leans out the mixture by allowing more air into circuit. I have an extended one ( the stock one is tucked up in float bowl that has to be adjusted with short screwdriver)that I adjust even needs adjustment between morning temps and afternoon temps when it get warmer, as far as blue smoke my guess would be valve guide allowing oil into combustion chamber
  8. Mellowyellow

    Mellowyellow XS650 Addict

    Thanks for the suggestions guys. Yamamunn i think your on to something with the valve guide because i also thought that the bike was running to lean so i took a look at the plug and it would indicate the opposite. Running to rich as its dark and with burnt oil but still dry burnt black. And i will forsure look into my hot start too that sounds like a good start.

    Last fall in my last ride the bike over heated (I could actually hear the rad boiling) i think it was my fault because typically im a fast rider but i was taking it easy because i could tell the valves needed adjustment and didnt want to blown anything up.

    As far as running the bike on the stand for 5 minutes i didnt realize it would over heat that fast.

    After 5 minutes on the stand it also boils in the rad and pukes out the overflow pretty excessive. If it was blowing white smoke i would believe its a head gasket but its blue.

    So my plan today if i get time will be to......

    -Adjust air screw
    -check hot start
    -and im going to buy a pressure tester and pressure up the rad to see if i do maybe have a small leak in the head gasket.

    Thanks again for the help guys.. i will let you know what i come up with.

  9. Mellowyellow

    Mellowyellow XS650 Addict

    I really want this thing fixed and out of the way. Ive got the xs ready for spring, the harley and the boys cr125 all set to go. Need this kx fixed so i can start on my new project (71 f250 with a cummins) should be fun.
  10. tscacadc

    tscacadc XS650 Enthusiast

    I have heard from a couple friends that Kaws heads get warped. I have a good friend that last years had to get his head milled and put a new gasket on. He was having a similar problem.
  11. Mellowyellow

    Mellowyellow XS650 Addict

    Ya i read that also.

    I also read that if you use a glass window (as a flat surface) and a sheet of emery cloth you can mill the head by hand with pretty good results.

    They say everything on the internet is true so it must be hahaha. I might try it because the only milling machine I have access to is way way out of spec and wouldnt dare try anything to precise with it.
  12. yamamunn

    yamamunn XS650 Enthusiast

    yes your plug would look like that if valve guides are leaking oil into the combustion chamber but the air/fuel ratio can still be lean. I do not think head gasket as you said blue smoke not white. oil is getting inside either past the valves or if your rings are beat. is your oil level down? wouldn,t be much as it will not take much oil to make the smoke
  13. Mellowyellow

    Mellowyellow XS650 Addict

    Ya it uses lots of oil. I have to put half a jug (500ml) every ride!
  14. Mellowyellow

    Mellowyellow XS650 Addict

    So I guess now i need to figure out new rings and a piston or just vavle guides?
  15. mick71b

    mick71b There are none so blind as those who will not see. XS650.com Supporter

    Total rebuild time! This is what happens next.
  16. Mellowyellow

    Mellowyellow XS650 Addict

    ya that would totally suck
  17. yamamunn

    yamamunn XS650 Enthusiast

    probably time for rebuild I put new piston and rings every 50 hours have hour meter installed on all my bikes/ generator also, while its apart check out valves do you know how many hours are on the kx?
  18. yamamunn

    yamamunn XS650 Enthusiast

    you can check head for warpage with straight edge and feeler gauges but doubt thats your problem
  19. Mellowyellow

    Mellowyellow XS650 Addict

    No idea how many hours but im guessing ive put 30hrs on it last year when i bought it and its an 06 so im thinking its probably over due for a rebuild. When i set the valves there were no markings on the shims so im guessing they were from the factory so i doubt the last guy did much with the engine.

    I guess its time to order some parts.

    -timing chain.
    -cam chain tensioner.
    -valve guides
    -head gasket.
    -hour meter

    ouch!!! haha
  20. yamamunn

    yamamunn XS650 Enthusiast

    cheaper/better now than if it blows up

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